Large non-domesticated mammals are typically anesthetized and immobilized for reasons of medical examination or treatment, or for reasons of physiologic or morphologic study or herd health assessment. Any such examination or study is impossible unless the animals are immobilized, because the non-domesticated nature of the animals makes it impossible to approach or safely handle them, even in captive environments such as zoological parks or animal preserves. Performing any procedure that may produce pain is also impossible unless the animals are anesthetized, because the animals will resist such procedures, even if the animals are substantially immobilized.
Because non-domesticated animals cannot be approached for injection by hand, it is necessary to remotely deliver an anesthetizing and immobilizing drug, typically from a single dart projected or shot from a gun at the distance which the animal will tolerate before fleeing, i.e. the flight distance. A dart is a syringe-like structure which has a drug-confining chamber and an attached hypodermic needle. When the dart impacts the animal, the hypodermic needle penetrates through the hair and hide of the animal and into muscle. An expulsion chamber containing compressed gas or a small explosive charge is activated upon impact and quickly forces the liquid anesthetizing and immobilizing drug from the drug-confining chamber through the needle into the muscle of the animal. The drug enters the bloodstream, and over a short time period anesthetizes and immobilizes the animal.
The flight distance which a non-domesticated animal will tolerate varies with the species and the environment. To accommodate lengthy flight distances, the dart should have a trajectory distance of about 70 meters with good accuracy. Any shorter range will not always be satisfactory because it is usually difficult or impossible to approach free ranging wildlife species any closer than approximately 35 meters. The trajectory range should permit sufficient accuracy to deliver the dart into the muscle mass of a shoulder or hind quarter of the animal, because impacting the dart with a bony area such as the rib cage or lower extremity will not allow the needle to penetrate adequately to deliver the full dose of the anesthetizing and immobilizing drug.
Increasing the velocity of a dart will increase its range and will contribute to its accuracy, but increased velocity of the dart increases the risk of excessive trauma or tissue wound to the animal from the impact of the dart. The risk of such a tissue wound is directly related to the kinetic energy of the dart, and the kinetic energy increases with the square of the velocity.
A dart injury in a free ranging animal is an ideal environment for clostridial species of anaerobic bacteria (the causative organisms of fatal clostridial septicemia) and other bacterial organisms to enter the blood circulatory system. The hair and hide of a free-ranging animal is a typical and natural environment for various organisms which are benign on the exterior of the animal, but which can be fatal upon entering the bloodstream. An example of such organisms are those which create tetanus (Clostridium tetani) clostridial septicemia or blackleg (Clostridium chauvoei), and anthrax (Bacillus anthracis). Such diseases may be fatal to the animal within 24 to 72 hours after entering the bloodstream. A high velocity impact from a dart creates a deep anaerobic protein rich environment conducive to the growth of these disease organisms. Therefore increasing the velocity of the dart is not usually an acceptable rationale to obtain improvements in range or accuracy. Excessive dart velocity can also result in fatal physical injury to the animal if it penetrates the thoracic cavity or into the internal organs of the abdominal cavity.
The weight of the dart also affects range and accuracy. A heavier weight dart will have less effective range than a lighter weight dart. The accuracy in placement of a heavier weight dart may be less than to a lighter weight dart, because the heavier dart may spend more time in trajectory and therefore fall more under the influence of gravity. A heavier dart will also create more tissue injury or trauma upon impact, resulting in more risk of disease from bacteria growth, as described above. The amount of tissue injury or trauma increases linearly with weight, rather than in relation to the square of the velocity.
One influence on the weight of the dart is the volume of the immobilizing and anesthetizing drug that it must carry. Larger volumes of the drug are heavier and require a larger dart. The weight and species of the non-domesticated animal contributes to the amount or volume of the immobilizing and anesthetizing drug that must be used. For example, an average adult white tailed deer (Odocoileus virginianus) weighs at least 50 kg, an average adult American black bear (Ursus americanus) may weigh 100-300 kg, an average adult moose (Alces alces) may weigh 200-300 kg, an adult North American elk (Cervus elaphus) may weigh 250-400 kg, and an average adult bison (Bison bison) may weigh 300-400 kg. Since a single dart must be effective in immobilizing and anesthetizing the animal, the dart must carry enough volume of the drug to achieve those effects. Although darts with a maximum capacity of about 5 or more ml are available, such darts are usually susceptible to the above described disadvantages of limited range and accuracy and excessive tissue injury. A dart with a drug-carrying capacity of 3 ml or less is preferred, because its reduced size usually avoids or minimizes the above described disadvantages.
Another factor which influences the volume of drug that the dart must carry is the potency of the anesthetizing and immobilizing drug. Combinations of drugs create synergistic anesthetic effects and allow lesser volumes to achieve greater effects in non-domesticated species. There are many different factors which influence the selections of the drugs in the combinations, such as the method of delivery, volume required, the duration and quality of the anesthesia, side effects, and the availability of antagonists for reversing the anesthetizing and immobilizing effect.
For example, xylazine, an alpha 2 adrenergic agonist, has been used to immobilize deer. Xylazine has also been combined with United States Drug Enforcement Agency (DEA) schedule II opioids such as etorphine or carfentanil, and has also been combined with DEA schedule III cyclohexamines such as ketamine and tiletamine, to synergistically improve efficacy and reduce drug volume. Medetomidine hydrochloride, another alpha 2 adrenergic agonist, has also been suggested as an alternative to xylazine, and has been tested in several deer species. Butorphanol tartrate, a morphine-based DEA schedule IV opioid, has been combined with medetomidine and xylazine for sedation of captive wildlife, but in so far as is known, butorphanol tartrate itself has been tested only as a post-surgical analgesic in deer. Azaperone tartrate, a neuroleptic sedative, has been combined with xylazine and/or fentanyl and with etorphine to immobilize deer but there are no known characterizations of the effects of the resulting anesthesia and immobilization.
Other potent opioid/alpha 2 agonist, opioid/alpha 2 agonist/dissociative anesthetic, opioid/alpha 2 agonist/neuroleptic tranquilizer, alpha 2 agonist/dissociative anesthetic and tiletamine/zolazepam combinations have also been used. Some of these drugs are reversible individually and in combination by the administration of antagonists.
Some of these synergistic drug combinations have been reported to create undesirable side effects, such as bloating and regurgitation, temperature regulation problems, hypoxemia, apnea/respiratory depression, hyperthermia, muscle rigidity, altered blood pressure, excitement, incomplete reversibility, and prolonged recovery times, among other things. These undesirable side effects occur despite achieving relatively adequate immobilization and anesthesia. As an example of the difficulties created by some of these undesirable side effects, any physical examination of an animal experiencing muscle rigidity is almost impossible or is accomplished only with great effort, despite the fact that the animal may be immobilized and anesthetized.
Mortality resulting from hyperthermia or respiratory depression is usually not an acceptable outcome from any medical or scientific study or examination. Since the animal must be released into the natural environment after completion of the examination or procedure, the animal is likely to be unable to move in response to flight-invoked stimulus or be unable to naturally protect itself if the animal remains partially sedated. Under such circumstances the animal is placed at an unacceptable risk of death or injury from its natural predators or from encountering natural environmental hazards such as cliffs and bodies of water.
A significant disadvantage of using known previous synergistic drug combinations is that the individual pharmaceutically active components are highly regulated DEA schedule II and DEA schedule III drugs. Governmental regulations govern the use of such drugs because of their potential for human abuse. Precise accounts of the volumetric quantity of the drugs used must be kept. A substantial administrative burden is involved in such accounting and other record-keeping. Governmental regulations also require legitimate users to keep the drugs secure from theft, which in practicality means that the drugs must be kept in very substantial locked safes. The record-keeping and safety regulations make actual use of substantial quantities of such prior synergistic drug combinations very difficult, and in some cases impossible during prolonged medical, physiological, morphological or herd health assessment studies carried out in the field or environment of free ranging non-domesticated animals.
Another important issue of any immobilizing and anesthetizing drug is the ability to formulate it quickly into doses of different potencies in the field, to accommodate different sizes of non-domesticated animals that may be encountered. To accomplish this, the drug must remain viable in a environment which does not permit special preservation methods and techniques, such as refrigeration. Animal studies may go on for days or weeks, and the immobilizing and anesthetizing drug must remain useful for the duration of such studies. Safety to the humans handling potent drugs is also an important concern, so that the drugs are not inadvertently taken up by humans.